Electric discharge device



March 30, 1948. T, HEHENKAMP 2,438,557

ELECTRIC DISCHARGE DEVICE Fil ed Feb. 26, 1945 /5 6 I ll 2 Irwverfl or": Theodorus Hehenk amp,

His Ahkor'neg.

Patented Mar. 30, 1948 ELECTRIC DISCHARGE DEVICE Theodorus Hehenkamp, Eindhoven, Netherlands, assignor, by mesne assignments, to General Electric Company, Schenectady, N. Y., a corporation of New York Application February 26, 1943, Serial No. 477,331 In the Netherlands December 10, 1940 Section 1, Public Law 690, August 8, 1946 Patent expires December 10, 1960 1 Claim. 1

In a device comprising an electric gas discharge tube (which term is here employed to refer not only to a discharge tube in which the discharge occurs in a filling constituted merely by gas, butalso to discharge tubes comprising a vapor filling or a filling constituted by gas and vapor) furnished with two incandescent electrodes. ne end of each electrode is connected in series with a contact of a bimetallic switch and the other end of each electrode, with the interposition of a choke coil respectively directly, with the terminals of the source of current. When the entire installation is energized the contacts of the bimetallic switch are closed so that a current is conducted in the choke coil and the'incandescent electrodes. One of the connecting conductors between tube and source of current includes the heating element of the bimetallic switch so that the contacts of the switch open after a lapse of a predetermined interval of time and the choke coil induces a potential pulse which assists in initiating an arc discharge in the tube. If initiation of the discharge occurs the bi-metallic switch is maintained open by the heating element but in the case of misfiring the bi-metallic switch closes again and the starting system attempts a re-cycling operation.

In this starting device the disadvantage exists that if the discharge tube is defective the automatically operating starting system continues to operate Without the possibility of an are discharge occurring. This not only may lead to damage of the starting device and circuit therefor but also may result in overheating the choke coil. This necessitates a choke coil of larger dimensions than those required for normal use or else assumes the risk that the choke may likewise be caused to deteriorate.

In addition, if this device is supplied with alternating current other effects may also be responsible for the occurrence therein of currents of inadmissibly high intensity. The originally equal emitting power of the electrodes may have changed, for example by the end of the life of the tube, in such a manner that in a given halfcycle of the alternating-current-supply the current is considerably lower than in the next-following half-cycle. This involves the occurrence of a direct-current component with the result that the choke exhibits a lower impedance than if an alternating current without direct-current component is conducted therein. Hence, the choke gives passage to a larger current with the result that it is subjected to intenser heating than in the normal use of the tube.

It is obvious that a current of undesired strength due to the occurrence of a direct-current component may occur even in the absence of an automatic ignition or starting system.

Similar difii-culties may also exist in other de-' vices in which a discharge tube is likewise con nected in parallel with part of a circuit connected to the source of current. Thus, ior example, devices are known which include a resonance circuit constituted by the series combination of inductance and capacitance, the discharge tube being connected in parallel with the inductance or with the capacitance and comprising an incandescent electrode which is included in the resonance circuit. When such device is connected in the circuit the resonance circuit has passing through it a large current which causes the said incandescent electrode to assume the emission temperature and sets up high voltages between the ends of the inductance and between the condenser electrodes. The discharge tube, after an arc discharge occurs, forms a'parallel branch conductor with part of the resonance circuit with the result that the current strength in this circuit falls off considerably. i

This device also presents the disadvantages heretofore' mentioned, since if an arc discharge does not occur in the discharge tube for any reason whatsoever there is the risk that the elements of the device may be caused todeterie crate, as in the case of the occurrence of a direct current component.

My invention relates to a device comprising an electric gas-discharge tube and a branch con-'- ductor in which, due to misfiring of the tube or as a result of the occurrence of a direct-current component when the tube is in use, a current may be conducted which is inadmissible on ac count of its value and/or duration and it has ior its object to avoid damage of the elements oi the device.

According to my invention, I provide a means which, when the said inadmissible current 00 curs, applies such a high voltage to a bridge whose interruption throws the device out of action, this "bridge has passing through ity'a current of higher intensity than the inadmissible current and is interrupted thereby.

According to my invention, I have found that it is impossible or else extremely difficult to con struct a cut-out or other kind of almost permanently interruptible bridge, for example a magnetically operating switch, which is interrupted by the current of undesired strength that occurs in defective tubes. The following effects may be I ec veitube nd mentioned as responsible for the difilculties thereby incurred: the inadmissible currents are often in the case of potential fluctuations of the current.

supply is substantially effective in that part of the circuit which is located outsidethe di schalrge tube and hence also in the cut-out. Eurther, it is not immaterial in what cre n ngs-en out has to operate, for exampl ingareem slight temperature differences inregard to the mean temperature prevailing there or in the open air where, apart from great;-temperaturexdififer ences, it may be exposed to the influence of windand mm. It is hardly possible to he supplier nf thedevice previously to take -the dorfdit" ifs into account. In devices in which starting the transformers or other voltage-increasing means. "'In' th'e'case of bridges arranged in the discharge sp .ce'foffthe gasdischarge tube, for example in .:,the";cesevof incandescent electrodes, an are dischar e may occur 'upon interruption of the bridge, .-in;;paralle1..withlthe aperture then formed inthe a-bridgeiandre-close the circuit. In order that in .suchcases the circuit will definitely be intertedQtheb'ridge according to my invention may comprise a cut-out located outside the discharge discharge tube is brought about by automatically operating ignition or starting systems the current ri to star in :iee en-erea er ha hez eerat ne cu ren with-en, inadmissibl direct l-1tibi.P.QS-

eu t nt-eomn en never eles i Sible f h ierees r nga u rent tbeqmainained e a rte lene h orztimezsioieexemple a .B huflil the e e rq esief; t e scha e tube her sumedvthe*emi on t mnerat re. "-J-Acfli ul ie z utli ed "-br-P i vi iee- ,mee s-v en byeth "h iq efie not inte nin e rby' t e: undes ed-cu ren el hut-bratcurr ntrwhi nmeyzb me lemu h .1 erran uh r-e za re u a rthe-seid amen ld ee :a thehridee; .t er s to flcw hmus he let re ult Til) --.te disms icn cor ine bridge ems l e denenden orth sb en h:.c n-- w i h thezumiee red cur ent ,OQQUISS-ED that t eder qe n heathr ivn -Qu rcf-e tlcne y F LE P iO -Pf 10. 1. 5 ne rid e; even if .n- @Qeeddz 1ents: may be expe ed more than ,s e he s-the c se deyices i whi hrthe iseberee De ec heses-dischar e tu space."

According to my invention, the means that cause. the .requisite'voltage to be effective in. the bridge .maybecoristitutedby atleast one thermal lswitcli ior. example bimetallic switch, whose heater is included in the operating circuitof the tube- .and /or..-in-that part of the circuit setting up the S arting-up voltage which is connected .in parallel. with. thedischarge-path.

lT-hermal switches have theproperty of becoming;operative at a greater or lesser speedaccordto the Ivalue of the current passing through theheater and iofnot comingv into play below a current intensity. The heaterfor such switches may be constituted :by impedances, 'ior example chokes, condensers, and/or resistances e ete mrem ei h I .o a-cir'eui e he ted th e l teeei'cu ren end-i -w iche -hig =w2l a 15 e icle lr set up: t r star in the d 9 eetebenth eeen isfir nerort etub en e u eu loneduetiennccmsin the taming. circuit whereasa directeurrent con $3 ?s .=e he wee-1y ee-9510mm W19?- A rging t my in e t onain his; civic the briee ma 'be r luded L n nam .orth sen.- necting lead between the discharge athg of tthe j be,and.the.sour e of currefit whic s el o htnestaitingcirc itf' s1. gas. .disd'ifit'gfi tubes the mey b te be sne' edla-la d seei qm th e e ee imie dencet e he mee s Jo eer e-. th t n, eele ee he V V ne r ng'er rep ec n thel ,eer d e he eswe 'd be h m e -W rk at two different points.

ve epteiee ie my nre t e is is m -meat flee meet n "the rid e be w n: he-"m llefi e h h-en ec onneet e ep e fthetube Q e n-Q e etes;maximally, s n hewlis rsng ered n emeee-J Q e he e emen o 9i... iceable witholl ds e s-th se e e wi he d seher etu e.

in eed: ibe ol ep ac me i e dee through whichflth'e undesired current passes.

.lln'a number or devices the-high current values necessary for starting .up occur in the same branch conductor .asthat in which also currents ojflundesired strength mayo'ccur asa result of. a

directiecurrnt component so that in such devices theii'se. of a single'means is sufii'cient. In ,devices having diverting Ipropertiesit is preferable that special. means should be provided at suitable pbintsl iorwany. effect responsible for unduly thigh currents,-it=being'often possible to use a far-reachii'igv [combination of the means. "In order to spare'the heater or the thermal switch it may be arranged in such manner that it t is' hot incl'uded. in the circuit Which comprises the; contacts of the switch. V "In order that my invention may be clearly under'sto odcand readily carried into efiect it will now held-ascribed more fully with reference to the accompanying. drawing in which lEigure 1 illustrates a circuit arrangement inaccordance with the invention, 7

.e li'igc 2 illustrates another embodiment of' the invention and p IFig-f3 illustrates;v a further embodiment in accordance with the invention.

Rig: 1v shows a device comprising ardischarge I lamp-- 1. This lamp may be of'well known construction and may constitute, .for example, a

low y-pressure mercury-vapour discharge tube nating'current and on the other hand to the elec- 7 W ld? B Of 'an-auXiliary discharge tube 9, where as the electroitlet is connected on the one: hand For higher voltages than the- :znetworkvoltage use may be made of step-up via an over-load cutout IIJ incorporated in the cap 5 to the terminal II of the said source of current and on the other hand to the electrode I2 of the tube 9. The auxiliary tube 9 comprises a gas filling, for example neon, at a low pressure, for example f 10 mms. of mercury, and the electrodes 8 and I2 are constituted by bimetallic strips which engage each other under the influence of the heat evolved by the discharge. The tube has such dimensions that it will operate at the full network voltage but will not operate at the operating voltage of the main discharge tube 2 at its electrodes. r

The device operates as follows:

Upon connection of the device to the source of current via a switch (not shown) the voltage of the source of current is effective between the electrodes 8 and I2 oi the auxiliary discharge tube 9. A glow discharge occurs in tube 9 and the electrodes 8 and I2 engage each other after a short time with the result that the electrodes 2 and 3 of the main discharge tube I have passing through them a large current which is only limited by the ballast or choke 6 and causes them to assume th emission temperature very quickly. Since the electrodes of the tube 9 have no longer heat supplied to them, the bimetallic strips cool and the electrodes are again disengaged, the circuit being thereby interrupted and a high voltage serving for starting up the lamp I being generated in the choke 6.

' When the lamp l is started, the full network voltage is no longer applied to the electrodes of tube 9 but only the operating voltage of lamp I so that the discharge in tube 9 is no longer initiated and the contact between 8 and I2 continues to remain in its normally open position.

In the case of misfiring of lamp I, the ignition or starting system starts a re-cycling operation. Should the lamp give out after repeated starting attempts there is the risk that choke 6 may deteriorate due to a large current that exists with short-circuited electrodes 8 and I2.

To avoid this, the choke 6 is provided with a bimetallic strip I3. This strip is connected'to that end of the electrode 3 which is connected to the electrode I2 and is constructed so that on the choke assuming a certain temperature the contact piece I4 engages the contact piece I6 which is connected to a tapping I5 of the choke.

In the case of misfiring of the lamp I, so that the network voltage, only reduced by part of the choke 6, becomes efi'ective in the electrically conductive bridge of the lamp I, which is constituted by the electrode 3 and the cut-out I0 connected in series with each other, this bridge has passing through it a very large current which brings about blowing of the cutout I 0 with the result that the ignition system is thrown out of action.

Excessive heating of the choke 6 may also occur if the electron-emitting power of one of the electrodes of the lamp I falls off. This may be due to the electrode concerned becoming bald, that is to say that the emitting material disappears from the core of the said electrodes. Due to this phenomenon less current passes through the discharge tube in the half-cycle in which the poorly emitting electrode acts as the cathode as compared with the half-cycle within which the properly emitting electrode acts as the cathode. As previously mentioned, this involves the occurrence of a direct current component as addition to the alternating current with the result that the choke on which magnetization is superposed by direct current allows the passage of more current than without direct-current component.

In this case also the bimetallic strip will bridge the points I4 and I6 and bring about the interruption of the bridge 3IIJ as soon as the temperature of the choke 6 assumes aypredetermined temperature. This ensures that the device is undamaged and the defective tube alone deteri orates.

In a number of cases the bridge to be interrupted depends upon the disintegration or destruction of electrode 3 alone which in such a case must have such dimensions as to blow upon engagement of the contacts I4 and I6. This, however, gives rise to the possibility of a discharge occurring between the ends of the electrode 3 which are located within the discharge space of the tube, which would result in the circuit that was interrupted by the rupture of the electrode 3 being closed again.

Here, the use of the cut-out IIl outside the discharge space of the tube ofiers a solution. The large current set up by the increased voltage passes through the cut-out III in any case irrespective of the occurrence or non-occurrence of a discharge between the ends of the electrode.

By the Way of illustration it may be mentioned that in one concrete case the normal currentstrength of the discharge tube I was 250 ma., whereas the electrodes 2, 3 while being heated up had passing through them a current of 450 ma, it being possible for the discharge current in the presence of a direct-current component to be 350 ma.

The arrangement of the cut-out in the common part of the supply circuit and the starting circuit of the tube I ensures that upon blowing of the cut-out ID the tube I is thrown out of action under any conditions.

Fig. 2 shows a device comprising a discharge lamp I! which may be, for example, an elongated low-pressure metal-vapor discharge tube. The tube contains singly heated incandescent electrodes I8 and I9. Laterally of the electrode I8 a cut-out 29 is arranged in the cap of the tube (not shown) outside the discharge space of the lamp and connected in series with the electrode I8. This fuse is included in the-common part'of the supply circuit and the starting circuit of the tube.

The electrically conducting bridge of the lamp I? which is constituted by the members I8 and 29 is included in a circuit which is connected to the terminals 2| and 22 of the source of alternating current and. which is constituted by chokes 23, 24 and a condenser 25 connected in series with each other. The two chokes 23 and 24 are generally arranged on a common iron core. The incandescent electrode I9 is connected, with the interposition of a choke 26, to the choke 23 and the condenser 25. This incandescent electrode is heated in a manner not indicated in further detail by a current which is substantially equal to the heating current of the incandescent electrode I8 and for this purpose may be coupled to the circuit of the electrode I9 for example by means of a transformer Alternatively, it is possible for the electrode I9 to be heated in series with the electrode I8 in that the connection between the condenser 25 and the point intermediate the chokes 23 and 26 is removed and the choke 26 is provided with an auxiliary winding which interconnects the free ends of the electrode I9 and the condenser 25 and is wound in such manner that-when a series ur nt nassins thr usmhoth-windiags .of the choke,. -.magnetic .nelds-z-counteracting :each other are setup. 7

. The device shown operates as follows:

When. the device isenergizedthe circuit constituted-by the series connection .of the choke coil 23,. the-condenser; ,25, therrbridge ,l.8'20 and the choke coil- 24-1 .is .connectedacross the source 'of alternating. current Jim-e22. The inductance of the chokes :23 and 24 and the capacitance of. the condenser .25 areso, proportioned that between the condenser electrodes'--.a -voltage occurs which causes. the electrodes .of the; tube to assume the emission temperature. Aiteranarcdischargehas occurred in tube 1| 1, tubel1 dorms-a shuntacross the condenser 2.5 so that the voltage 'iaOI'QSS .the terminals of the latter decreases. At the same a time, the current which flows throughthe-series connection of the. chokesand the condenser also decreases so that .the .,incandescent electrode J [8 which at this point is also heated by thezdischarge current also ,has .asmaller current passing through it. .The discharge current .flows :towancls the tube 1 11 via the chokes 23 and 23011 the one vhandand the choke24 on the-other hand.

In the case. of-misfiring ofthe tube I'lthecondition ofv .high' :voltages. and large current *would subsist. The occurrence rota direct-current componentwilllikewisecause a largecurrent to be setrupwinsthe circuit f-the-.discha1ge.tube. In both cases the current strength is. higher than in the normal operating condition so that the 'device is likely tube dama ed. v

= To avoid this the heater r21 of a bimetallic switch is included between the choke 23 and the terminalof thesource-aof current. Starting with a given currentstrength which is obviously hi herethanthe normal current strength at this point .the heater .21 causes the contacts .28- and 29 to engage each other. The con-tactpieceZB is connected via .abimetallio. stripill toa point between the terminal 2 I vandthe element 21, whereasrthe contact piece-29 .is connectedtoa point betweenthecondenser- 25 and the.- electrode 28 so.that-,theecut-outifl is only connected to the voltage ofithesource of. current :2 22 with the interposition of-the chokefl and the incandescentlclectrode 18. Obviously, it will bepossible iorl thi .yoltage at-t-hecut-outin 'toebe raised or lowered ifnecessary; with the .use of well-known means.

,In the easeillustrated the heaterv 21 is included in the-circuitarrangement that the large current required for the-interruption of the bridge l8- -2lldoes not .flowthrough the element- 21 itself. Any damage ofthiselement isthusavoided. As a matter. of fact. after the-contacts-28,. 29 have been closedv the bimetallic-switch has notsupplied to. it..anyfurther heat energy but. in practically occurring cases .the contacts are maintained closedfora sufliciently long timeto enable the increased voltage to interrupt the bridge meanwhile.

In oneconcrete case, in a :tube not yet started thelvoltage across, the choke 23 was "60 .volts; across the condenser .25, .330 volts across the bridge i8.+2ll,.l2 volts;z-and across the choke 24, 100 volts, the. current. p sing through the series circuit being .400 ma. =With normally. operating tube the. currentpassing through the tube I1 and the-choke. hadan-intensity of 250 -ma., through the. chokes 23and 2,4,of 150.ma. and through the condenserl25, of 225-Ina, the voltage across 23, 34,25,16 and i-.8+2-0:being respectively, 28, 48, 199,.. 150and-2 volts. Therbimetallic zswitch had such .a..characteristic curve thatswith a current 01190 ma. through the heater 21m contacts are ZS- ZStbeing closed, the currentpassing through the bridge was 1.5 amp. The interruption of the bridge ensued !7 sec. after the closure of the contacts-28--29. The source ofcurrent 2l-.22 was an alternating current network of 50 cycles and a voltage'of 220 volts.

Fig, 3 shows a device comprising agasdischarge tube 50 which may be, for example, a sodium-vapour lamp and .is provided with two incandescent electrodes -31 and 32. .These electrodes are interconnected via a choke 33 and a condenser. The other end of theelectrode 3| is connected via aballast or ch'oke 35 to .the terminal 36 of a sourceof alternating current, and the other end of theelectrode32 :via a cutoutr31 to the other'terminal 38 of the source of current. l I

The-inductances or the chokes 35 and 33am} the capacitance of the condenser 34 are such that at least when the electrodes have assumed the emission- -temperature a voltage sufiic-ient for the ignition of the discharge path of the tubeSQ between the electrodes 3| and-32 occurs. After the discharge-path-has been ignited tube 50 forms a shuntacross the series connection. of the choke 33 and the condenser 34 with the result that the voltage between those ends of this series connectionwhich areconnected to the tube falls to'the operating voltage of the tube and at thesame time theh igh starting current passing through 33 and .34 similarly falls off considerably. ,In the case of misfirlng of the tubeithe condition of :high voltages and currentszis maintained, whereasupon the occurrence of a direct-current component the current conducted in the tube the current passing through thezchoke35.

was 225 ma., through the tubefit, 240ma. and through the series combination of 33 and-:34; 56

ma. r

As revealed thereby; the device may be arranged in such manner that .the current passing through the choke 35 is substantially iridepen'dentcf whether or not the tube is started. In contradistinction thereto the current passing through the members'33 and'34 connected inpar-allel with the tube is dependent on the ignition or -non ignition of the tube. Itwill, however, "be clearly evident that the occurrence of adirect-current component increases the current passing through the choke 35.

The device shown therefore includes two bimetallicswitches 39 and-.40 .for which-the chokes 35 and 33respectivelyv serveas heaters. The-two switches are adaptedto connect thetapping 45 of the choke 35, via the contacts 4!, 42 and.43, M

supply-circuitxand ignition or starting circuit of the tube 50 where the current has practically the same value when the tube is in normal use as in the case of the tube not being started.

I claim:

In combination, a supply circuit, an electric discharge device having a pair of filamentary electrodes, a ballast connected between one terminal of said circuit and one of said electrodes, an over-load cut-out device connected in series relation with said device between the other terminal of said circuit and the other electrode, a glow discharge switch of the bi-metal type connected across said electrodes and completing a preheating circuit for said electrodes through which said electrodes are energized from said circuit in series relation with said ballast and said cut-out device, and a bridge circuit connected between said other electrode and an intermediate tap of said ballast and including a thermal device having normally open contacts and being responsive to the current conducted by said ballast 10 r for transmitting current from said supply circuit in an amount sufiicient to operate said cut-out device upon repeated attempts of saidswitch to initiate conduction by said discharge device;-

THEODORUS HEI-IENKAMP.

REFERENCES CITED The following references are of record in the 0 file of this patent:

UNITED STATES PATENTS 

